Optolong UHC (Ultra High Contrast) is a light pollution filter for use in severely light polluted urban area. It selectively enhances emission from nebulas and suppresses the transmission of light pollution sources. UHC enhances the transmission of nebulas emissions and reduce background brightness mostly dominated by light pollution. It has narrower passband than CLS (City Light Suppression) and thus it is the better choice of imaging under severely light polluted areas due to its more rigorous light pollution suppression. Its wider passband towards the red end of the visible spectrum makes it exceptionally suitable for hydrogen emission dominated objects such as M42 Great Orion Nebula.

UHC selectively cuts out light pollution emission. For example, mercury vapor lamps, high and low pressure sodium vapor lights and skyglow caused by emission from neutral oxygen in our atmosphere. Among the emission lines enhanced are OIII (496, 500nm), H-beta (486nm), NII (654, 658nm), H-alpha (656nm) and SII (672nm).  

The major difference between Optolong CLS and CLS-CCD is CLS-CCD has a built in UV/IR cut feature. Emissions below 450nm (UV) and beyond 700-1000nm (IR) are cut off. Some astrophotographers choose CLS-CCD to eliminate an extra layer of UV/IR filter in their imaging chain, normally installed by factory on CCD/CMOS cameras. This could help eliminate halos around bright stars due to multi-reflections in some cases.

The Rosette Nebula above was imaged with 110ED (0.8x reducer), Canon EOS500D (modded) and Optolong UHC filter. It's a stack of 20x5 mins exposure at ISO1600 under a orangish sky. 

Highlights

• 95% transmission at major nebula emission lines
• 0.1% transmission* at off-band at Na (589nm), Hg (435nm, 578nm). 
• Multi-layers anti-reflection coating
• Precise and sharp roll-off at light pollutant lines
• 2 mm filter thickness (1.25", 2" and 77mm) | 1mm (clip series)
• Made on Schott substrate
• Finely polished to 1/4 wave accuracy
• Surface quality: 60/40 (MIL-O-13830 standard)

*equivalent to OD3

Recommended applications

• Monochrome & one-shot-colour CCD/CMOS camera
• Deep sky colour imaging, particularly emission nebula or DSO emitting in the H-alpha, H-beta, O-III and S-II lines 

Available in sizes

• 1.25" (26mm clear aperture)
• 2" (45mm clear aperture)

Coating technologies

• Multi layers anti-reflection coating
• Non cementing optical substrate coating
• Electron-beam gun evaporation with ion-assisted deposition coating technology to enhance coating durability and resistance to scratching as well as stability on central wavelength such that passband does not deviate with temperature change
• Planetary rotation system offers high precision and homogeneity of coating surface ensuring high value on passband transmission and off-band blocking. 

Filter cell technologies

• CNC machined with aerospace grade aluminium
• Black anoidised finish and extinction treatment to prevent refection
• Laser engraved fade-free wordings 

We care about delivering your filter in perfect form and thus every Optolong filter sits on a high density sponge carton lining and packaged in highly rigid plastic PP case with high pressure EVA case lining. 

User gallery

Milky Way at Victoria Harbour, Hong Kong Author: Vincent Cheng September 2015, Hong Kong Camera: Canon EOS-M modded Telescope/Lens : 11mm f/2.8 @ Tokina AT-X 116 PRO DX AF 11-16mm  Filter : Optolong UHC EOS clip-on Tracking Mount : Sky-Watcher Star Adventurer Autoguide : none Total Exposure Time : 30sec X 13frames (foreground 8s + 2s HDR) ISO800 w Dark Frames, Bias Frames process w PI, PS5

Left: With Optolong UHC, right: without Sky glow is effective removed in the left image Author: Jeff Dai November 2015 85mm f/1.8 ISO12800 8s

About Optolong

Optolong is a brand dedicated for astronomical filters R&D and production under Kunming Yulong Optical & Electronics Technology Co. Ltd. Yulong is a professional manufacturer of high quality filters since 1999. Yulong has passed ISO9001 quality certifcation and all products meet ROHS standard authorised by SGS test. 

Their major equipment include ultra clean room, five precise vacuum coating machines, Shimadzu UV-VIS-NIR spectrophotometer, 12 sinks ultrasonic cleaning machines and grinding/rolling/cutting machines.

Optolong filters only use the best glass — German's Schott glass as the substrate which has an industry leading level of flatness which is crucial to minimise the occurence of halo and ensure high quality image.